One of the more common technologies for treating waste water is based on a settling process, often using fixating agents such as hydroxide and sulfates. The fixating chemicals are added to water in a settling tank to absorb or otherwise transform the contaminants into materials which settle to the bottom of the tank. This technology uses comparatively simple equipment and permits the processing of large volumes of waste waters, without adding materials which would result in an environmentally undesirable effluent stream. In fact, in some systems, no fixing agents are used because the contaminants are sufficiently large to settle in the tanks. However, in many cases, use of ordinary settling processes fails to reduce contaminant concentrations to levels low enough to meet desired requirements, without using excessive amounts of materials, over a protracted processing time. In addition, traditional settling processes often require extremely large settling reservoir to provide adequate settling time for smaller particles.
In addition to settling tanks, conventional treatment processes to remove undissolved solids include the use of settling tanks, clarifiers, centrifuges, gravity filters and pressure filters. The processed effluent, freed of undissolved solids by such techniques or combined techniques still requires further processing to remove dissolved solids. Conventional approaches to removing dissolved solids include precipitation initiated by pH adjustment or reagent addition, flocculation and settling, micro-filtration and precipitate concentration through centrifuge or plate press action.
The composition of filter elements for such techniques, depending on the process employed and particulate matter to be removed, can be perforated or slotted metal, or polymeric elements such as polypropylene or polyester cartridges. High density inorganic adsorbent materials (HDIA) can also be used to promote solid separation in the flocculation phase. Typically, these materials have been natural or synthetic low density aluminum silicates called zeolites, used to capture positively charged ions of the filtered elements. In addition, beds of sand or other particulate matter are used in a mechanical filtration process called polishing. The contaminated water is passed one or more times through the bed with or without periodic backwashes to flush the entrapped residue upstream for flocculation and micro-filtration.
These known procedures and techniques for separating and removing aqueous based contaminants greatly reduce the environmental hazards. Unfortunately, however, a high degree of desired effluent purity may require repeated cycling through the individual filtration steps with associated storage, time, and cost penalties, if such a high level can be achieved at all. As a result, available conventional systems can suffer one or more of the short-comings discussed above.